Known conventional rotation angle detecting devices include a throttle position sensor which detects the rotation angle of a shaft of a throttle valve (that is, the open/close angle of the throttle valve) when the shaft is rotated in association with the open/close operation of the throttle valve placed within an aspiration path of an internal combustion engine (see, for example, Patent Document 1).
The rotation angle detecting device realized by the throttle position sensor described in Patent Document 1 is mainly formed of a rotation shaft (rotation member) which rotates in response to the rotation of the shaft, a pair of magnets which rotates around the rotation shaft in synchronization with the rotation of the rotation shaft, a magneto-electric conversion element which is placed at the back of the rotation shaft and detects a change in the magnitude of a magnetic flux (the magnitude of a magnetic field) in association with the rotation operation of each of the magnets, a magnetic member of generally cylindrical cap shape including an annular portion having an insertion fixing portion for inserting and fixing a lower end portion of the rotation shaft and a tubular portion covering each of the magnets, and a housing of generally cylindrical cap shape including an annular plate portion having a penetration portion through which the rotation shaft passes and a cylindrical portion covering the outer periphery of the tubular portion and accommodating the magnetic member.
Since the rotation angle detecting device described in Patent Document 1 includes the housing which rotatably supports the rotation member serving as the rotation shaft and the cover accommodating the magneto-electric conversion element, the rotation angle detecting device has the problem in that the number of parts constituting the device is increased to require higher assembly cost and parts cost to result in an increase in the overall cost.
To address the abovementioned problem, the present applicant has proposed a rotation angle detecting device capable of reducing cost in which a magnet rotating with a rotation member in response to the rotation of an object under detection is provided, a magneto-electric conversion element detecting the magnitude of a magnetic flux changing with the rotation of the magnet is used to output a detection signal according to the rotation of the object under detection, and a metal member rotatably supports the rotation member is formed integrally with a housing through insertion molding (see Patent Document 2).